This invention relates to wireless local area networks, and more particularly to a method and apparatus for using multicast packet addressing for use by base stations in wireless local area networks communicating with wireless local mobile units.
Wireless local area networks (WLANs) use infrared (IR) or radio frequency (RF) communications channels to communicate between portable or mobile computer terminals and stationary access points or base stations. These access points are connected by a wired or wireless communication channels to a network infrastructure which connects groups of access points together to from a local area network (LAN), which can include one or more host computers. In turn, the LAN can be connected to another larger network such as the Internet and the World Wide Web (Web). Several protocols, including the IEEE 802.11 standard, xe2x80x9cWireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specificationsxe2x80x9d (as in place on the filing date of this application) have been designed to standardized WLAN communications. Such standardization is useful for optimizing user requirements, including spatial layout, response time, loading and throughput requirements of the network.
xe2x80x9cRoamingxe2x80x9d terminals are mobile units that can associate with any access points (AP) associated with a WLAN and seamlessly move from AP to AP. Each roaming terminal analyzes received signals from access points in its vicinity and associates with a single access point. Communication with an access point connects a terminal with the LAN and therefore with external networks such as the Internet. The region around an access point can be referred to as a xe2x80x9ccellxe2x80x9d. Roaming terminals can move from cell to cell and remain connected to the LAN and any other network to which the roaming terminal has connected.
A mobile unit user typically roams from one AP to another AP. It takes a certain delay period for the mobile unit to be associated with the new AP before the mobile unit is able to receive data packets. During this delay period, the user will experience a disruption of communication because an association with the new AP has not yet been established. The disruption causes data packets to be lost or become useless due to the time lost during the association period. While this disruption is acceptable for non real time services such as data file transfer, it is not acceptable for real time services such as real time video or phone conversations.
The number of simultaneous telephone conversations that can be handled between a single access point and multiple mobile units within range and associated with the AP is limited by the processing speed of the AP. Since conventional APs may not distinguish traffic classes (e.g. voice and data traffic), packet delay on voice traffic channels may result in degraded quality of service.
Streaming multicast video systems send a video stream to a multicast group of computers using a specific compression rate. These systems currently lack the ability to scale up or down the bit-rate according to the connection speed available and/or computing power of the receiver. This may result in inefficient bandwidth utilization because the source would have to send multiple multicast streams to each homogenous group of computers.
When a mobile phone user, having a fixed IP address, roams to a foreign subnet, they cannot be located since they have left the home subnet. In current mobile IP systems, the calling party communicates with the mobile computer through the mobile""s home subnet. Although the subnet knows the location of mobile, there is an unacceptable time delay. While this may be acceptable in non real-time services such as file transfer, it is not acceptable in real-time services, such as voice, since the long time delay causes the phone conversation to become non-interactive.
Although the applications described above relates to multicasting as applied to layer 2 or MAC addresses associated with communications over a wireless link of a network, the same concepts can be applied to the wired segments of the network and layer 3 or IP addresses. By way of background, it is useful to discuss the framework associated with communications between APs, such as that considered by IEEE P802.11 Task Group f as part of the evolving IEEE P802.11 standard. One issue is the requirement that stations must have a layer 3 address that is local with respect to the layer 3 address of the AP, e.g., the station must have an IP address that is valid in the subnet in which the AP is operating. How the station obtains this local address is immaterial to the AP and the inter access point protocol. A station might perform a DHCP renew on reassociation, or it might be running operating under Mobile IP. Knowing that all the stations in a BSS will have local layer 3 addresses reduces the complexity of the task of delivering frames for the stations via the wired network or distribution system. That task can now be done by the normal routing functions available to any station on the subnet. How a message is distributed with the Distribution System Service, as defined in the IEEE 802.11 standard.
The requirement that the station have a local layer 3 address is problematic with respect to any long-lived TCP connection which would be lost when the station moved from one subnet to another, unless Mobile IP is used. However, in most of today""s applications, the connections are not long lived. Examples of applications that might be adversely affected (without Mobile IP) are FTP and Telnet.
The invention relates to a method of operating a data communications network including a plurality of mobile or stationary access points and optionally at least one host computer connected to said access points, and a plurality of remote mobile wireless units, at least some of the mobile units being capable of communicating with at least one of the access points when located within a predetermined range there from and being normally associated with and in communications with a single one of such access points, each mobile unit having a unique user address. The invention provides establishing communication and association between the mobile units and the access points utilizing a packet frame addressing protocol including a multicast address; receiving in one of the access points at least two distinct sequences of packets addressed to at least two mobile units respectively associated with the access point; forming a frame, with a multicast address including the addresses of the at least two mobile units, in the access point and including in the data field of said frame unicast packets addressed to each of the at least two mobile units; and transmitting the frame to the mobile units by the one access point.
Another aspect of the invention relates to a method and system for managing transparent roaming in a wireless LAN system using multicast IP. By using multicast IP to establish an association between a mobile unit and an AP, a mobile unit is able to roam from one cell to another without experiencing a disconnection or delay in communication from packet to packet.
In yet another aspect of the invention, a method and apparatus is disclosed for distributing and updating software in a mobile unit wireless LAN using multicast IP. The software is transmitted throughout the network using a multicast IP address, and any mobile unit on the network receives the information by simply xe2x80x9ctuningxe2x80x9d into the IP address at its own convenience.
In another aspect of the invention, a method and apparatus is disclosed for streaming multicast scalable video to heterogeneous computers in a wireless LAN. The source transmits multiple bit rate video streams to computers with different bit-rate requirements. Each computer is able to reconstruct the video stream according to its own requirements.
In another aspect of the invention, a wireless LAN using multicast IP is configured for managing mobile phones. The IP address of a mobile unit at a home AP is mapped to a multicast IP address, the mobile unit roams to a foreign AP, a user calls the mobile unit using the IP address related to the home AP, the mobile unit receives the IP request, and the mobile unit transmits back the new IP address that it was assigned when it roamed to the foreign AP.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.